Evidence that the geneuvrB is indispensable for a polymerase I deficient strain ofEscherichia coli K-12

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Abstract
Conclusive evidence in presented to show that the geneuvrA is dispensable, but theuvrB is indispensable for anEscherichia coli strain carrying genepolA1. We constructed strains E139 (sup-126 polA1 uvrB59) and E159 (sup-126 polA1 uvrA43) where mutationspolA1, uvrB59 anduvrA43 are amber mutations and mutationsup-126 is an amber suppressor mutation effective at 30°C but not at 42°C. At 42°C, strain E139 is inviable but strain E159 viable whereas both are viable at 30°C. Revertants of E139 viable at 42°C occurred spontaneously at a frequency of about 3×10-4. One of the revertants was shown to be caused by suppressor mutation, designatedspu, rather than back mutation of the geneuvrB59 orpolA1 or amber suppressor mutation. Viabilities of the revertants varied from 10-3 to 1.0 at 42°C compared with those at 30°C. At 42°C, all the revertants with normal viabilities at 42°C were non-filamentous in contrast to the filamentous character of E139. However, strain E159 was viable at 42°C despite its filamentous character. We conclude that the geneuvrB is involved not only in excision repair but also in normal growth in apolA background.

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